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Robust frequency coding sequence estimation of the Costas discrete frequency-coded (DFC) waveform signal is an important task for radar reconnaissance interpretation in radar electronic warfare. However, due to the unknown waveform characteristics of the signal, conventional frequency coding sequence estimation algorithms are not applied in noncooperative target scenarios, especially those with a low signal-to-noise ratio (SNR). Therefore, based on the hidden Markov model (HMM), a frequency coding sequence estimation method for Costas DFC waveforms is developed in this article. Through associating the time–frequency distribution of the Costas DFC waveform signal with the HMM, the frequency coding estimation of the waveform can be transformed into the sequence decoding problem of the HMM. In the proposed algorithm, an effective decoding model library can be obtained after HMMs are initialized and trained. Then, the time–frequency observation sequence of the Costas DFC waveform signal is used to select the optimal decoding model from the library. Finally, the Costas frequency coding sequence of the waveform is estimated by the Viterbi algorithm. Simulation experiments verify that the proposed algorithm has strong decoding capability and robustness for various Costas DFC waveforms under different SNR conditions. [ABSTRACT FROM AUTHOR]

A periodic mirror-reflected circular-polarized (CP) leaky wave antenna (LWA) with dual-beam scanning in dual polarization types is reported in this communication. The unit cell of the proposed antenna consists of two oblique stubs that are orthogonally separated (90°) to create a circular polarization. In order to achieve better CP (axial ratio (AR) < 3 dB) and beam-scanning characteristics for the periodic CP antenna, a new method of adding a groove at the junction of stubs within the unit cell is introduced. To realize dual-beam scanning in dual circular polarization, a metal via is added at the end of the antenna to generate a mirror reflection. A mirror-reflected structure is fabricated and measured. The measured results show that the right-handed CP (RHCP) scanning range of the incident beam is −31° to −8° and 5° to −14°, and the left-handed CP (LHCP) scanning range of the corresponding reflected beam is 31°–6° and −6° to −15°. The measured results are in good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

In this communication, a phased array antenna with an integrated metasurface is designed to achieve wideband and wide-angle scanning. Generally, the coupling between adjacent elements changes significantly as the scanning angle increases, resulting in limited scanning coverage. Two mutually perpendicular metasurface slabs are designed to achieve wide-angle scanning. The mutual coupling is reduced by properly tuning the dimension of the metasurface. Two perpendicular linear arrays were fabricated to verify the design. The measured 3 dB beamwidth of the active element pattern (AEP, in the array environment) with the integrated metasurface is about 150° in the E-plane and 109° in the H-plane, which is suitable for wide-angle scanning. The simulated and measured results indicate that the beam can scan from −78° to 78° with a 3 dB gain fluctuation in the E-plane array and a wide frequency range from 10 to 12.5 GHz (22.2%). In the H-plane array, the scan angle ranges from −69° to 69° with a 3 dB gain fluctuation and a relative bandwidth of 11%. [ABSTRACT FROM AUTHOR]

In this letter, a 1-bit wideband reconfigurable unit cell for transmitarray applications in Ku-band is proposed. The unit cell consists of a Vivaldi structure (transmitting), a phase shifter, and a microstrip Yagi structure (receiving). Based on the current reversal mechanism, a pair of reverse mounted PIN diodes was introduced to obtain the required phase resolution (two phase states: 0° and 180°). The unit cell is fabricated and measured using a specific waveguide simulator. The measured minimum insertion losses are 1.58 and 1.61 dB for State I and II, respectively. The insertion loss is less than 2.58 dB (1 dB bandwidth) from 14.88 to 17.28 GHz for State I, and less than 2.61 dB (1 dB bandwidth) from 14.73 to 17.25 GHz for State II. The 1 dB bandwidth of the unit cell is about 15%. The measured phase difference remains 180°, and the maximum error is only 3.8°. [ABSTRACT FROM AUTHOR]

The interrupted-sampling repeater jamming (ISRJ) is a kind of intrapulse coherent deception jamming, it produces false-target peaks, which obfuscate the real target detection and tracking. In this article, a novel recognition method is proposed to identify the false-target peaks caused by ISRJ. The proposed method is realized via the integration decomposition of pulse compression, and the intermediate data in pulse compression are extracted to identify the false-target peaks. Due to the time-sharing transmit–receive antenna of the jammer, the jamming signal is short or discontinuous pieces compared with the real echo. This intrinsic property provides important feature for jamming identification. In the proposed method, a variance value is generated from the intermediate data, to evaluate the temporal energy distribution evenness of the signal component corresponding to each target peak. Real target echo corresponds to small variance whereas the jamming signal corresponds to large variance. In this way, false-target peaks caused by jamming signal can be identified efficiently. Besides, the computational cost of the proposed method is low, thus, it is suitable for real-time applications in practical radar systems. Numerical experiments under different jamming parameters demonstrate the promising performance of the proposed false-target recognition method. Moreover, Monte Carlo simulations under different SNR levels verify the reliable classification capability of the proposed method. In summary, this article provides a new perspective for ISRJ identification, and it is also the proof-of-concept example for other potential applications concerning integration decomposition. [ABSTRACT FROM AUTHOR]